This is an application to develop and test methodological innovations related to "Youthnet," a randomized controlled trial (RCT) that is designed to test, with a clinic-based sample, the efficacy of computer-based, tailored, interactive condom use messages for increasing positive outcome expectancies towards condoms, condom use norms, self-efficacy for condom negotiation and use, and condom use with non-main sexual partners. For this methodological supplemental application, we will focus on three methodological aims: Supplemental Aim 1: To replicate the clinic-based Youthnet RCT with a probability sample recruited exclusively on two separate sites on the Internet. Supplemental Aim 2: To test, using the Internet sample, the psychometric properties of four behavioral scales developed for this study; outcome expectancies for condom use; condom norms; self-efficacy for condom negotiation and self-efficacy for use. Supplemental Aim 3: To compare a) recruitment and retention rates and b) baseline and outcome data on outcome expectancies, norms, self-efficacy for condom negotiation and use and condom use of the clinic based and Internet-based samples. The study questions we will answer with this supplement include: [unreadable] 1. Will people aged 18-24 recruited through banner ads online enroll in a study about HIV/STD risk? [unreadable] 2. Will persons enrolled online return for a one-month booster session and a two-month follow- up session and with what level of attrition? [unreadable] 3. Are the psychometric properties of the study instrument the same for an online sample compared to a clinic-based sample? [unreadable] 4. What is the efficacy of the intervention for increasing condom use with non-main partners for the online sample? [unreadable] [unreadable]